1. Field of the Invention
The present invention relates to a polymer composition having excellent compatibility composed of (A) starch and (B) vinyl alcohol polymer having an alkyl group of 4 to 50 carbon atoms at the terminal.
The present invention relates further to a polymer composition having excellent compatibility composed of (A) starch, (B) vinyl alcohol polymer having an alkyl group of 4 to 50 carbon atoms at the terminal, and (C) polyvinyl alcohol.
The present invention relates also to a textile sizing agent which gives yarn good weavability. More particularly, it relates to a textile sizing agent to give yarn good weavability, which is composed of (A) starch, (B) vinyl alcohol polymer having an alkyl group of 4 to 50 carbon atoms at the terminal, (C) polyvinyl alcohol, and (D) oil for textile sizing.
2. Description of the Prior Art
A mixture of starch and polyvinyl alcohol (abbreviated as PVA hereinafter) has a usage for warp sizing and paper sizing because it is water-soluble and good in film-forming performance and natural starch is water-soluble and readily available at a low price. However, it has some disadvantages: A mixed aqueous solution of starch and PVA is so unstable as to cause the separation of solutes, because of the poor compatibility of starch and PVA, which are both polymeric compound. In addition, it forms a film which is poor in transparency and other film properties.
For the improvement of the compatibility of starch and PVA, many attempts were made to use various kinds of modified starch (including starch derivatives such as etherified starch, esterified starch, and cationized starch; and decomposition products of starch such as oxidized starch and dextrin). Starch derivatives are expensive and decomposition products of starch have a disadvantage ascribed to their lower molecular weight than natural starch. That is, a mixed aqueous solution of a decomposition product of starch and PVA is stable but does not provide a film of good properties. In other words, these starch derivatives and decomposition products of starch are not satisfactory in compatibility with PVA.
On the other hand, it is known that modified PVA copolymerized with monomers having long-chain alkyl groups of 4-20 carbon atoms has improved compatibility with natural starch. ( Japanese Patent Laid-open Nos. 4544/1981 and 55440/1981.) A mixed aqueous solution of the modified PVA and starch is stabler than that of unmodified PVA and starch. Nevertheless, it easily gels and does not form a film of satisfactory properties. Furthermore, the modified PVA is not effective for the above-mentioned modified starch.
As for PVA, there is known a process for producing a vinyl alcohol polymer having a long-chain alkyl group at the terminal. (See Japanese Patent Publication No. 1831/1973 and Japanese Patent Laid-open No. 108207/1983.) However, nothing is known about the compatibility of this vinyl alcohol polymer with starch.
In the meantime, there is an ever-increasing demand for a warp size having higher performance than before. The warp size has become necessary for high-speed weaving and production of high-quality textiles since the advent of modern looms including shuttle looms, gripper looms, rapier looms, water jet looms, and air jet looms, which are used for weaving natural fibers (such as cotton and wool), semisynthetic fibers ( such as rayon, acetate and etc.) , and synthetic fibers (such as nylon, polyester, and acrylic).
To make a sizing agent for warp sizing, starch, PVA, and acrylic size are used individually or in combination with one another. They are also used in combination with oil for textile sizing and carboxymethylcellulose. PVA is most popular among them, and it is used in the form of completely saponified PVA, partially saponified PVA, anion-modified PVA, or cation-modified PVA or other modified PVA. Modified PVA in which a hydrophobic group is copolymerized is also known( as disclosed in Japanese Patent Laid-open Nos.55440/1981 and 174683/1983). They are all intended to improve the adhesion of a sizing agent to hydrophobic fibers such as polyester and nylon, thereby to improve the cohesive force and abrasive resistance and to reduce the yarn hairiness.
There are known processes for producing a vinyl alcohol polymer having a long-chain alkyl group at the terminal( as disclosed in Japanese Patent Publication No. 1831/1973 and Japanese Patent Laid-open Nos. 108207/1983 and 102946/1984). It is also known that the vinyl alcohol polymer has improved abrasive resistance due to a low coefficient of friction(as disclosed in Japanese Patent Publication No. 22218/1969) and the vinyl alcohol polymer can be used for the surface modification of molded items(as disclosed in Japanese Patent Publication No. 18258/1971).
A warp sizing agent for spun yarns is usually composed of PVA and starch. PVA is preferred because of its stable quality attributable to its being a synthetic polymer, its good film-forming performance and ability to form film of good properties, and its good adhesion to fibers. Starch is preferred because of its low price and its ready availability. The disadvantage of this sizing agent is that PVA and starch are poor in compatibility with each other because they are both polymeric compounds. Therefore, a mixed aqueous solution of PVA and starch is so unstable that PVA and starch readily separate from each other. Moreover, the aqueous solution of PVA and starch becomes poor in sizing performance after standing for a couple of days to such an extent that it cannot be used again.
PVA and starch are often used in combination with acrylic size, oil for textile sizing, and/or CMC. Oil for textile sizing is used to (1) make smooth the yarn surface, (2) promote the infiltration of the size solution, (3) make the sized yarn hygroscopic, (4) impart antistatic properties, (5) prevent the yarn from sticking to the drying cylinder of the sizing machine, (6) make the yarn soft, and (7) improve the yarn handling. Oil for textile sizing includes various vegetable oils, paraffin wax, and surface active agents. Paraffin wax and vegetable oils are generally used where (1),(5),(6) and(7) are the major objectives. They are emulsified and dispersed into water by an emulsifier (a nonionic or ionic surface active agent). Nevertheless, they are essentially poor in compatibility with PVA and starch and the sizing solution thereof is poor in stability. The film formed from the sizing solution is not uniform in quality and poor in strength and elongation, although it softens the yarn. Elongation is so low that the film as a whole is brittle and poor in abrasive resistance. Thus, the sizing agent is not suitable for warps to be woven into high-quality textiles or to be woven on a high-speed loom such as air jet loom.
There is a warp sizing agent based on anion-modified PVA, cation-modified PVA, or PVA copolymerized with a hydrophobic group. This sizing agent, when dissolved in water by heating, forms a stable sizing solution; but the stability is not still satisfactory. The film formed after drying of the size solution is not completely uniform. Therefore, this sizing agent is not satisfactory in weavability where high-quality textiles and high-speed looms are involved.
Another means to improve the compatibility is to add an acrylic size to a mixture of PVA, starch and oil for textile sizing. However, the improvement in compatibility is insufficient.